docs: def allowed(self, **kwargs):
          """
          Get all available sender settings which could be used in "from" parameter of POST messages method.
          Returns :class:`Source` object.
  
          :Example:
  
          allowed = client.sources.allowed()
  
          :param country:  Return sender settings available in specified country only. Optional.
          """
          resp, instance = self.request("GET", self.uri, params=kwargs)
          return self.load_instance(instance)